Studies of long-term survivors of cancer treated with radiation therapy and chemotherapy have led to important insights into carcinogenesis. In the past year, we have completed the analysis of a study of patients treated for Langerhans cell histiocytosis. This group was selected because they frequently are treated with single agent epipodophyllotoxins. In two groups of Italian and German patients, the risks were strikingly different, with a several hundred-fold risk of leukemia in the Italians but no leukemias occurring in the Germans. The leukemias occurring in the Italians were all promyolocytic and lacked the characteristics described for epipodophyllotoxin-related leukemias. The risk of leukemia in the Italians may be modulated by genetic risk factors, since promyolocytic leukemia is more common in individuals of Mediterranean descent. Followup of a cohort of children treated for ALL and their siblings revealed that the survivors did not experience substantial longterm health effects, second cancers, or adverse effects on child bearing. A study of radiation-related neural tumors was also initiated in a cohort of individuals receiving head and neck irradiation in childhood.